How Google Works: A Mobile-First Perspective on Ranking Signals
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How Google Works: A Mobile-First Perspective on Ranking Signals
- 1. How Google Works A Ranking Engineer’s Perspective Paul Haahr SMX West March 3, 2016
- 3. Mobile First
- 4. Features • spelling suggestions • autocomplete • related searches • related questions • calculator • knowledge graph • answers • featured snippets • maps • images • videos • in-depth articles • movie showtimes • sports scores • weather • flight status • package tracking • …
- 5. Ranking
- 7. What documents do we show? What order do we show them in?
- 9. Two Parts of a Search Engine • Ahead of time (before the query) • Query processing
- 10. Before the Query • Crawl the web • Analyze the crawled pages • Extract links • Render contents • Annotate semantics • … • Build an index
- 11. The Index • Like the index of a book • For each word, a list of pages it appears on • Broken up into groups of millions of pages • At Google, these are called “shards” • 1000s of shards for the web index • Plus per-document metadata
- 12. Query Processing • Query understanding and expansion • Retrieval and scoring • Post-retrieval adjustments
- 13. Query Understanding • Does the query name any known entities? • [san jose convention center] • [matt cutts] • Are there useful synonyms? • [gm trucks]: “gm” → “general motors” • [gm corn]: “gm” → “genetically modified” • Context matters
- 14. Retrieval and Scoring • Send the query to all the shards • Each shard • Finds matching pages • Computes a score for query+page • Sends back the top N pages by score • Combine all the top pages • Sort by score
- 15. Post-retrieval adjustments • Host clustering, sitelinks • Is there too much duplication? • Spam demotions, manual actions • …
- 16. What do ranking engineers do? (version 1) Write code for those servers
- 17. Scoring Signals
- 18. Signal • A piece of information used in scoring • Query independent – feature of page • PageRank, language, mobile friendliness, ... • Query dependent – feature of page & query • keyword hits, synonyms, proximity, …
- 19. What do ranking engineers do? (version 2) Look for new signals. Combine old signals in new ways.
- 20. Metrics
- 21. “If you can not measure it, you can not improve it.” –Lord Kelvin (sort of)
- 22. Key Metrics • Relevance • Does a page usefully answer the user’s query? • Ranking’s top-line metric • Quality • How good are the results we show? • Time to result (faster is better) • ...
- 23. Higher results matter • “Position weighed” • “Reciprocally ranked” metrics • Position 1 is worth 1 • Position 2 is worth ½ • Position 3 is worth ⅓ • Position 4 is worth ¼ • …
- 24. What do ranking engineers do? (version 3) Optimize for our metrics
- 25. But where do the metrics come from?
- 26. Evaluation
- 27. How do we measure ourselves? • Live Experiments • Human Rater Experiments
- 28. Live Experiments
- 29. Live Experiments • A/B experiments on real traffic • Similar to what many other websites do • Look for changes in click patterns • Harder to understand than you might expect • A lot of traffic is in one experiment or another
- 30. Interpreting Live Experiments • Both pages P1 and P2 answer user’s need • For P1, answer is on the page • For P2, answer is on the page and in the snippet • Algorithm A puts P1 before P2 ⇒ user clicks on P1 ⇒ “good” • Algorithm B puts P2 before P1 ⇒ no click ⇒ “bad” • Do we really think A is better than B?
- 32. Human Rater Experiments • Show real people experimental search results • Ask how good the results are • Ratings aggregated across raters • Published guidelines explain criteria for raters • Tools support doing this in an automated way
- 35. Two Scales • Needs Met • Does this page address the user’s need? • Our current relevance metric • Page Quality • How good is the page?
- 36. Mobile First
- 37. Mobile First Rating “Needs Met rating tasks ask [raters] to focus on mobile user needs and think about how helpful and satisfying the result is for the mobile users.”
- 38. How do we make it mobile-centric? • More mobile queries than desktop in samples • Pay attention to user’s location • Tools display mobile user experience • Raters visit websites on smartphones
- 39. Needs Met Rating
- 40. Needs Met Rating • Fully Meets • Highly Meets • Moderately Meets • Slightly Meets • Fails to Meets (Following examples are from Rater Guidelines)
- 41. Fully Meets
- 43. Highly Meets
- 45. Moderately Meets
- 46. Slightly Meets
- 47. Fails to Meet
- 49. Page Quality Concepts • Expertise • Authoritativeness • Trustworthiness
- 50. High Quality Pages • A satisfying amount of high quality main content • The page and website are expert, authoritative, and trustworthy for the topic of the page • The website has a good reputation for the topic of the page
- 51. Low Quality Pages • The quality of the main content is low • There is an unsatisfying amount of main content • The author does not have expertise or is not trustworthy or authoritative for the topic • The website has a negative reputation • The secondary content is distracting or unhelpful
- 53. Ranking engineers • Team of a few hundred computer scientists • Focused on our metrics and signals • Run lots of experiments • Make lots of changes
- 54. Development Process • Idea • Repeat until ready: • Write code • Generate data • Run experiments • Analyze • Launch report by Quantitative Analyst • Launch review
- 55. What do ranking engineers do? (version 4) Move results with good ratings up. Move results with bad ratings down.
- 56. What Goes Wrong? (And how do we fix it?)
- 57. Two kinds of problems • Systematically bad ratings • Metrics don’t capture things we care about
- 58. Bad Ratings
- 59. [texas farm fertilizer] • User is looking for a brand of fertilizer • Unlikely to want to go to the manufacturer’s headquarters • Rater average called map of headquarters almost “Highly Meets”
- 60. Patterns of Losses • Look for things we think are bad in results • Either live or from experiments • Create examples for rater guidelines
- 62. Missing Metrics
- 64. Low Quality Content in 2009-2011 • Lots of complaints about low quality content • But our relevance metric kept going up • Low quality pages can be very relevant • We thought we were doing great • ⇒ We weren’t measuring what we needed to
- 65. Quality Metric • Gets directly at the quality issue • Not the same as relevance • Enabled development of quality-related signals
- 67. What do ranking engineers do? (version 5) Fix rater guidelines or develop new metrics (when necessary)
- 68. Thank you!
- 69. Questions?